Bias Problem

andy

I have a G 6000 that I can finally adjust the DC offset on but not the Bias current.  I connect the meter to the left channel (right does the same) and turn the unit on.  Before the relay clicks, I see 300 mV or so on the meter.  When the relay clicks on, the meter drops to .5 mV and then bleeds off gradually to 0.  The adjustment pots do nothing.

I've already checked everything on the PS and driver board against specs and another working unit and I just don't know what else to look at.  What can cause this type of problem?

Thanks.

Where/how are you connecting the meter?  Bias should never be 300 mv and should not be affected at all by the relay position.

- Pete

Pete, I'm using the TPs illustrated in the manual.  Two in front of the relay and two to the right side.  If I recall correctly (I'm at work now), the two in front are positive for the L and R and the two on the side are negative for L and R.  The 300 mV I said I was getting is only on the meter until the relay clicks on.  After it clicks, the voltage drops immediately to .5mV and then gradualy to zero.  I did find one bad 2SD313 transistor on the board and I was able to adjust the DC offset ok after that.  This transistor had a diode across the base and emitter that was bad too so it got replaced.  There are several of these transistor/diode combinations on the G6 but the rest seem to check out ok.

Sorry, I think that transistor was a 2SD813 instead.  Hell, I can't remember unless I'm looking at it.

Hello drbacklash,

I don't know anything about a G6000 but I just had a very similar problem with an au-317. It turned out to be the 150ohm fuse resistors, might have nothing to do with your problem.

forums/sho...d.php?t=172292

Compact1060, thanks for the tip.  I've checked all the PS resistors against the manual and replaced those that were questionable but I will go over them again with a keener eye on the FRs.  I believe I remember there were some on the driver but I'm not sure about the PS.

Thanks for taking the time to help.